VARIOUS, 



terior structure of the rock can alpne decide be* 

 tween sections which cross at right angles, which 

 are those which denote the position of the beds. 

 I have already mentioned what I thought of the 

 origin of the fissures which thus cut the beds, 

 and I shall elsewhere refer to it again. 



" I have distinguished four very distinct shades 

 in the transition of these schisti to granites. 



" The first layers of schistus, where some al- 

 teration is observed, assume plates more wavy, 

 brighter, more resembling mica; but they have 

 otherwise the same properties with the others. 



" The next are still more waved, plates of real 

 mica are observed, and besides a mixture of' 

 quartz, which yields fire with steel, although the 

 rock still effervesces with acids. Veins of a black 

 substance are observed in this same rock, bright, 

 composed of little rhomboids, which appear to 

 be the crystallisation of the purest substance of 

 the schistus ; for these crystals dissolve with ef- 

 fervescence in acids, without leaving any percep- 

 tible residue; and yet they very easily melt 

 under the blow-pipe into a greenish and trans- 

 parent glass, which sinks on the point of the 

 glass tube. 



" The third shade is a real quartz, mixed 

 with a little mica, and which does not efFer- 

 I vesce. 



o 2 



